1. Field of the Invention
Embodiments of the present disclosure generally relate to renewable energy power systems and, more particularly, to a method and apparatus providing a smart junction box in photovoltaic (PV) system.
2. Description of the Related Art
The worldwide growth of energy demand is leading to a durable increase in energy cost. In addition, it is now well established that the fossil energy reserves currently being used to generate electricity are rapidly being depleted. These growing impediments to conventional commercial power generation make solar modules a more attractive option to pursue.
Solar modules, or photovoltaic (PV) modules, convert energy from sunlight received into direct current (DC). The PV modules cannot store the electrical energy they produce, so the energy must either be dispersed to an energy storage system, such as a battery or pumped hydroelectricity storage, or dispersed by a load. One option to use the energy produced is to employ inverters to convert the DC current into an alternating current (AC) and couple the AC current to the commercial power grid. The power produced by such a distributed generation (DG) system can then be sold to the commercial power company, or used to offset local consumption of electricity by local loads.
PV modules within an array only generate equal amounts of power if exposed to a uniform amount of sunlight. However, should a single module be shaded (e.g., by a tree or cloud) or module become nonfunctioning, the power generated is inefficiently transferred and may adversely affect the shaded module. For example, the operating current of the overall series string approaches the short-circuit current of the singular shaded module and the overall current becomes limited by the shaded module. The extra current produced by the unshaded PV modules then forward biases the remaining PV modules.
If the series string is short circuited, then the forward bias across the unshaded PV modules causes a reverse bias on the shaded module. Thus a large number of series connected PV modules may cause a large reverse bias across the shaded module, leading to large dissipation of damaging power into the shaded module. Bypass diodes placed in the junction box have been used to protect the shaded PV module, however such diodes can dissipate an excess of 10 W when energized. The dissipation leads to high elevated temperatures in the junction box and possible thermal run away of the diodes.
Furthermore, continued power generation and conversion when a PV module is damaged may lead to arc faults which are extremely dangerous. The DC PV modules will continue to provide energy into a short circuit or an arcing circuit as long as the PV modules continue to be irradiated with light, potentially leading to a fire near the damaged PV module. The aforementioned dangers and necessary protective measures compound in complexity and risk as the PV module array grows in number and size.
Therefore, there is a need for a method and apparatus for a low cost, intelligent system for protecting and monitoring PV module operation.